The development of drive mechanisms for the Stirling engine in automotive use has followed the evolutionary development of the piston and cylinder assembly. The earliest piston and cylinder arrangement is known as a piston and displacer combination, each operating as a separate reciprocating element either within a common cylinder or within adjacent cylinders for thermal cycling gases therebetween. Single crank drive mechanisms were employed with such early piston-displacer arrangements; however it was not until the development of the rhombic drive that this piston-displacer arrangement became successful for automotive use. The most important contribution of the rhombic drive was the ability to provide for complete balancing, a feature not easily attainable in a machine with a crank-connecting rod mechanism and having separate piston and displacer elements.
With the need for greater engine efficiency, the double acting piston system was developed (sometimes referred to as the Rinia arrangement) whereby the displacer elements were eliminated; one side of each piston would provide a displacing function and the other side of the piston would serve as the conventional piston. In this manner each piston would operate during a complete cycle as both displacer and power piston. This required, of course, the connection of the upper expansion space of each cylinder to the lower compression space of the adjacent cylinder by means of a passage containing the heater, regenerator and cooler.
The invention herein is concerned with Stirling engines of the double acting piston cylinder arrangement. Two drive mechanisms have been utilized with the double acting piston arrangement. The first and earliest was that of the single crankshaft with suitable cranking arms interconnecting the pistons and the crankshaft. In some cases, the cylinders were arranged in an in-line configuration, but this required several heater head assemblies which additionally required a complex fuel control system. In others, the pistons and cylinders were been arranged in a V-configuration with the crank arms or connecting rods interconnecting with the single crankshaft; this demanded that the cylinders be spaced equal distances along the single crankshaft which also dictated a relatively wide spacing between the upper ends of the cylinders. Such wide spacing prevented a compact diametrical configuration for the engine heater head and severely inhibited the use of such design within an automotive packaging environment.
The second type of drive mechanism utilized with the double-acting pistons is that of the swash plate. This drive mechanism typically requires a cluster of pistons with their piston rods extending generally parallel to the output shaft, the piston rods connect with a crosshead mechanism which in turn contact a swash plate or wobble plate which tilts and rotates to convert the reciprocal movement of the piston rods to a rotary output motion. The rotary output motion is imparted to a central output shaft connected thereto. Unfortunately, the output shaft is in line with the piston rods and thus adds to the overall engine length. This is in opposition to the natural transverse direction of the output shaft in a crank engine.